Combustion control



June 6, 1939. v R. w s 2,161,361

COMBUSTION CONTROL Filed July 21, 1936 5 Sheets-Sheet l EMA-fir Laws I WvQfwma June 6, 1939. R, gw s 2,161,361

COMBUSTION CONTROL Filed July 21, 1936 5 Sheets-Sheet 2 W IL INVENTOR. Boa/Fer laws 2/ BY M m 9* M ATTORNEY-5'.

June 6, 1939. w s 2,161,361

COMBUSTION CONTROL Filed July 21, 1936 5 Sheets-Sheet 3 amaze June 6, 1939. R. LEWIS COMBUSTION CONTROL Filed July 21, 1936 5 Sheets-Sheet 4 lb INVENTOR.

fcdfiser LEW/s BY MW '1 M ATTORNEY? June 6, 1939. R. LEWIS COMBUSTION CONTROL Filed July 21, .1936

5 Sheets-Sheet 5 INVENTOR. BY @aE/ar zzw/s Patented June 6, 1939 UNITED STATES PATENT OFFICE COMBUSTION CONTROL Application July 21,

2 Claims.

This invention relates to control devices, and more particularly has reference to a method and apparatus for controlling the rate and efficiency of combustion in a furnace. While by no means 5 limited to the boiler field, it will be described with reference to power or heating boilers which operate underforced and induced draft, or under forced and natural draft.

Prior devices'and' methods of this general character have been open to serious objection. In the first place, many of the devices heretofore used have been" of the so-called positioning type, in which the various valves are set in definite positions in accordance with the steam pressure, and 1 5 in which, after the Valves are adjusted in any given position, there is no compensation for any change in air or fuel pressure.

Even in the so-called proportioning controls,

in which the actual amounts of air and fuel fed to the furnace are attemptedto be proportioned to the steam demand, there reside certain'disadvantages. In general, these last types of controls do not operate to effect optimum economies of I fuel, due to their principle of construction and operation, and particularly because there is a time lag between any variation in the control factors and the actual change in the element controlled. Furthermore, the prior controls have been relatively expensive to manufacture and rather difficult to operate.

To overcome the above objections is one of the objectsof my invention.

' Another object is to provide a device and method whereby fuel and air are supplied to a furnace in a definite ratio to each other to secure maximum combustion efficiency, and in which the rate of combustion is proportional to a condition of the medium being heated.

Yet another object is to provide a control by 46' which fuel is fed to a furnace in accordance with a condition of the heated medium, a forced draft is maintained in a definite ratio to the fuel feed,

and the pressure Within the combustion chamber is maintained substantially constant.

Afstill further object is to provide specific means for achieving the foregoing objects.

It willof course be appreciated that the specific form of apparatus disclosed in the drawings and described herein is susceptible of various modi- 50 fications, but the basic concept of my invention embraces 'anincrease'or decrease in the fuel supply as'the necessity for combustion increases or decreases/and-the maintenance of the proper amount of air in the combustion chamber tom- .51 sure*optimum=combustion efficiency More spe 1936, Serial No. 91,754

cifically, I contemplate a balancing of the amount of fuel fed to the furnace with a condition of the heated medium, a balancing of the fuel feed with the intensity of a forced draft, and the maintenance of a substantially uniform pressure in the combustion chamber.

In the accompanying drawings depicting one specific embodiment of my invention, and in which corresponding numerals refer to the same parts:

Figure 1 is a side view of my invention applied to a' conventional boiler;

Figure 2 is a fragmentary detailed view in elevation of the front of the control cabinet, showing the respective pivoted beams;

Figure 3 is a detailed view of the fuel control beam and its associated elements, and a diagrammatic sketch of the circuits for the control of the fuel feed, showing in heavy lines the automatic circuit closed to increase the fuel supply;

Figure 4 is a view of the same beam, but showing the circuits'for manually controlling the supply of fuel;

Figure 5 is a detailed view of the forced draft control beam and its associated circuits, and showing the beam in circuit closing position to increase the forced draft;

Figure 6 is a view of the combustion chamber control beam or stack damper control beam, and its associated circuits showing both circuits open;

Figure 7 is a vertical sectional view of the manometer actuated by the pressure in the forced draft wind box;

Figure 8 is a detailed view of the preferred arrangement of contacts for the forced draft control beam and stack damper control beam.

This invention is generally similar to the invention disclosed in my copending application, filed November 18, 1932, Serial No. 643,231, now Patent No. 2,049,707, and finds particular application in the case of a furnace operated under forced and induced draft or under forced and natural draft.

It will be observed that in the specific embodiment illustrated in the drawings, an application of this invention to a furnace in which the fuel is in gaseous form has been shown, and in *which the control factors are: the pressure of the steam in the steam header, the pressure of the fuel in the fuel header, the pressure in the forced draft wind box, and the pressure in the combustion chamber of the furnace.

It will be readily appreciated, however, in view of the prior art, and particularly in view of the disclosure of my above-mentioned co-pending application, that the specific apparatus herein disclosed may readily be modified for use in a solid fuel or liquid fuel furnace; and that the fuel control may be governed by the temperature, or flow, or liquid level of the heated medium, or any other condition thereof; that some condition of the fuel feed other than the fuel header pressure may be substituted; and furthermore, the forced draft factor may be some condition other than the pressure within the forced draft wind box, such as, for instance, the velocity of air flow.

It will also be noted that the invention is shown as applied to a forced and natural draft model, but it will of course be apparent that it may be used with equally beneficial results in a forced and induced draft furnace. Various other modifications or applications of the invention will suggest themselves to persons skilled in the art, and it is to be distinctly understood that I am to be bound merely by the scope of the appended claims.

Referring particularly to Fig. 1, there is disclosed a furnace provided with a combustion chamber section I and a boiler section 2. Steam is withdrawn from the boiler by means of a steam header 3, and the flue gases pass through a furnace outlet 4 to a stack, not shown.

As stated above, the particular embodiment disclosed in the drawings shows a furnace operated by a gaseous fuel which is supplied by a suitable main 5. The fuel passes through a control Valve 6 into a manifold I, and then by line 3 to the burner orifice (not shown) in the combustion chamber. A valved by-pass 9 may be provided around control valve 8. Also, a manually operable valve l I may be inserted in the line 8 to regulate or shut off the particular burner supplied by such line.

Of course the furnace may be provided with a plurality of burners all fed by the-manifold 1.

Itshould also be pointed out that the invention may be applied to a battery of boilers, as for example, when such batteries receive their fuel through a common control valve 6, discharge the flue gases into a common breeching, and a forced draft is supplied through a common Wind tunnel. In such event, however, it is usually necessary to provide suitable valves and dampers to maintain the proper ratio between the fuel and the air supplied to, and the flue gases exhausted from, the several furnaces, or by providing other control elements to regulate such factors individually or in groups. When such valves and dampers are initially set, the battery is then operated as a unit by the control shown in the drawings.

The air supporting combustion is furnished by a forced draft which passes through a wind tunnel l2 extending up to a forced draft wind box and thence through the burner (not shown) to combustion chamber l. The forced draft fan is not shown in the drawings, and a conventional type of fan may be employed which may be driven by electricity, steam, or other appropriate power.

There is tapped into the steam header 3, a steam line l3 which extends to the control cabinet and which terminates in a conventional diaphragm manometer H! as disclosed in Figures 2 through 4. In this element a lug I5 is mounted upon the diaphragm l6, and is adapted to move upwardly with an increase in the steam pressure within the boiler and to move downwardly with a decrease in the boiler pressure. While the line [3 is shown tapped into the steam header 3, it

will of course be appreciated that this line may be tapped into the boiler tubes proper. Also, as stated above, some other condition of the heated medium may be the control factor, such as demand, rate offlow, temperature, liquid level, etc.

The line ll is tapped into the fuel header 1 and likewise extends to the control cabinet l0. Within the control cabinet, and not shown in the drawings, the line I! is split to form two lines Ila and [1b, which extend to two manometers l8 and [9, respectively, as disclosed in Figures 2 through 5.

As best shown in Figure 3, the manometers are made up of a casing 2!, open at the upper end. An inverted casing 22 slidably fits within the casing 2|, and a body of mercury 23 is provided to form a liquid seal. Of course, any other suitable sealing liquid may be employed. The line I 1a or llb is tapped into the base of the casing 2! and by means of a tube 24 communicates with the interior of casing 22 above the level of the mercury 23. A knob 25 is provided on the top of casing 22. It will be observed that the buoyancy of casing 22 is a function of the pressure inside of the casing 22, which of course is the pressure of the fuel in the header 1.

A line 26 is tapped into the forced draft wind box near the burner. control cabinet l8 and is joined to a manometer 21 which, as, best shown in Figure 7, is made of a casing 28 containing a body of mercury 29 as a sealing medium. The casing 28 is carried by a bracket 36, and floating in the mercury is an:

inverted bell member 3!. A tube 32. is threaded in the discharge end of the line 26 and extends through the casing 28 and mercury seal 29 into' the upper reaches of bell 3i. It will therefore be noted that the pressure existing in the wind box is transmitted to the interior of the bell 3|, and that the bell .il thereby exerts a buoyant tendency varying with the pressure in the wind box.

A line 33 extends from the combustionchamher to the control cabinet in and is tapped into the bottom of a manometer 34 which. may be constructed in accordance with the principle of manometer 2]. It will be appreciatedz lib-akin accordance with the present theory of boiler operation, the pressure within the combustion chamber is preferably (though not necessarily) a negative pressure, less, than; atmospheric, whereas the steam pressure, the fuel pressure and the forced draft wind box; pressures will be all positive. Nevertheless. all of the manometers M, i8, i9, 21 and 34 will exert forces which will vary with the respective pressures to which they respond.

There is positioned in the forced draft wind tunnel I2 a damper 35 provided with an arm 36. A link 31 extends from the arm 36 to a crank 38. The crankGB is driven, through suitable reduction gearing 39, by a reversible motor 40.

Therefore the motor may be operated to open or closed by a door 51.

this invention.- In such event, the motor and arm 38 might regulate a'rheostat; to control an electric motor for the forced draft fan, or to operate a valve or other control means for a steam or other type motor for the forced draft fan.

In the furnace outlet 4 there is positioned a damper 4| provided with an operating arm '42. A link 43 connects arm 42 with a crank 44. The crank 44 likewise is operated, through suitable reduction gearing45, by a reversible electric motor '46. Therefore damper 4| is controlled by the operation of motor 46.

While not shown in the drawings, it will of course be appreciated that thefurnace pressure may be controlled by the useof aninduced draft fan... When such a fan is employed, its speed may be varied to control the furnace, or the fan may be run at a. constant speed and the furnace pres sure controlled by a damper on either the inlet or outlet side of such fan.

The valve 6 in the fuel feed line is provided with an arm 41 which in turn is operated by crank 48 through alink 49. The crank 48 is rockedby a reversible motor 56 which is also provided with suitable reduction-gearing. The

motors 40, 46 and 56 are allprovided with adjustable limit switches (not shown).

A conduit 5| carries from the control cabinet the wires forthe circuit of motor 46; conduit 52 carries the wires for motor46 and conduit 53 carries the wires for motor 50.

,Referring particularly to Figure 2, it will be noted that the control cabinet I0 is provided with four compartments, 5,4, 55 and 56, and a switch andterminal. compartment which is shown as Compartments 54, 55 and 56 are provided with doors 58, 59 and 6|, which are normally closed.

I ncompartment 54 there is located a so-called fuel control beam 62 which, as best shown in Figure 3, is pivotally mounted in anti-friction bearingson a bracket 63. The beam 62 is provided with a rail 64 on which is slidably mounted a weight 65. Furthermore, weights 66 are carried bythe beam 62 by means of a -depending rod The beam 62 carries a conductor (not shown) which is connected to a contact block 68, insulated from the beam proper by suitable material 69. .The beam 62 is adapted to be balanced between, or to oscillate between, two stationary contacts H and 12, which are adjustably spaced by means of set screws 13. The extent of movement of beam 62 between the stationary contacts H and I2 may therefore be varied.

Manometers l4 and I8 are carried by a rail 14 mounted within compartment 54, and a guide rail 15 also providesfurther'supportand maintains the manometers vertically disposed. Manometers l4 and I8 are adjustable longitudinally upon the rail 14.

It will be noted, therefore, that both the weights 65 and 66 and the relative positions of manometers l4 and I8 are adjustable. The spacing of manometers I4 and I8 determines the ratio between variations in the steam pressure and the rate at which fuel is supplied the furnace; and weights 65 and 66 are for the purpose of maintaining a balanceof the beam at the particular pressure decided upon; For instance, if it is desired to increase the operating pressure in the boiler, weight 65 may be moved to the left in Figure 3 or additional weights may be imposed upon depending rod 61;- or if these are not sufficient, then manometer I4 is moved to the right on rail 14, and manometer I8 is readjusted.

In operation the various elements are so adjusted that the beam 62 is balanced between contacts H and 12 for a given boiler pressure. When so adjusted the fuel is being fed at just the rate to maintain the desired boiler pressure. If the pressure drops below the determined amount, the force exerted by lug [5 of manometer 14 against the beam 62 will be decreased, and the beam will drop so that contacts 68 and 12 are closed. This serves to operate motor 56 in a direction to further open fuel valve 6. This results first in an increased pressure within the fuel header 1, and then the increased combustion effects an increased generation of steam which will either return the pressure to the desired point, or compensate for the increased demand on the boiler, or both. However, upon an increase in the pressure of fuel in header I, resulting from the opening of valve 6, the force exerted by manometer I8 is increased, throwing the beam back into balance and stopping any further opening of the valve.

Assuming that the pressure in the boiler exceeds the desired pressure (either from a decrease in demand, or from the just-described operation), the increased force exerted by manometer M will throw the beam 62 out of balance and engage contact 68 with contact II. This will reverse motor 56 to decrease the flow through valve 6. The reduction in fuel flow causes a decrease of pressure in fuel manifold I, and consequently a reduction in the force exerted by manometer l8. Inasmuch a beam 62 is supported by the combined forces of manometers l6 and I8, the circuit between contacts 66 and H will be thereby broken,and the beam returned to a balanced position intermediate contacts 'H and 12.

As best shown in Figure 5, a beam 16 is located in compartment 55 and is mounted on a standard 11 by means of anti-friction bearings. The standard I! is carried by rod 18 which also supports manometers l9 and 21. A guide rail l9 is likewise provided, and, as in the case of the fuel control beam, the fuel pressure manometer I9 is adjustable upon rod 18 in order to maintain the desired ratio between the fuel feed and the air input to the furnace. A weight 8| is adjustable upon a rod 82 carried by the beam, and serves to balance beam 16 between adjustable contacts 86 and 81.

Itwill be observed that the manometers l9 and 21 are disposed on opposite sides of the fulcrum point of beam 16, and it will also be noted that the manometer 21 is positively joined to the beam by'means of a screw 83 extending from the inverted bell 3| through a slot in the beam and a nut 84 threaded thereon.

Beam. 16 carries a conductor (not shown) which is connected to a spring contact 85. Beam 16, when the furnace is operating for a period with a given fuel input, is adapted to be balanced so that contact 85 lies intermediate the adjustable contacts 86 and 81.

Beam 16 controls the circuits of the damper motor 40 and thereby serves to regulate the forced draft. Assuming that the supply of fuel has been increased by virtue of a drop in steam pressure in the boiler, the fuel pressure in fuel manifold I is thereby increased. Such increased pressure is transmitted through lines I1 and 11b to manometer l9, which thereupon exerts a greater force on beam 16 in a counter-clockwise direction.- Therefore a circuit between contacts 85 and 8! is established which operates motor 40 in one direction to open damper 35. Upon opening of damper 35 the pressure within the forced draft wind box I2 is increased, and thereby manometer 21 increases its force upon beam I6 tending to re-establish the balance of the beam between contacts 86 and 81. The operation of the forced draft unit upon a decrease in fuel pressure will be equally apparent.

Within the compartment 56 (Figures 2 and 6) of control cabinet I there is located a beam I04 which controls stack damper M and consequently the pressure existing within the combustion chamber. This beam is mounted on anti-friction bearings in a standard I05 which in turn is mounted upon a rail I06. A guide rail I0! is likewise provided to effect additional support. A weight I08 is mounted on a projection I09 from the beam, and is longitudinally adjustable on such projection to secure the necessary balance of the beam under operating conditions.

The manometer 34 is mounted upon the rail I06, and is secured to the beam I04 by means of 2. lug III and nut H2. The manometer 34 is of generally similar construction to manometer 21,

' but is somewhat larger in view of the fact that itoperates at a lesser pressure. Also the sealing medium employed in manometer 34 may be oil instead of mercury, as in the case of manometer 21.

The beam I04 is likewise provided with a conductor (not shown) and with a flexible contact II3. When the beam is in balance this contact lies intermediate adjustable contacts H4 and H5. When the beam is thrown out of balance, one or the other of contacts H4 and H5 is contacted by contact II3.

Upon any increase in the combustion chamber pressure, the manometer 34 causes beam I 04 to make a contact between contacts H3 and H4. The circuit so established causes motor 46 to open damper 4| to thereby lower the pressure in the combustion chamber.

Upon a decrease below the normal of the combustion chamber pressure, contacts H3 and. I I5 will engage to operate the motor 46 in a reverse direction to close damper 4|. Upon closing of the damper the pressure in the combustion chamber will increase until the normal pressure is againv attained.

It will be noted that the beam I04 serves to maintain the pressure in the combustion chamber substantially constant, and thereby prevents the infiltration of unrequired air. The exact pressure to be maintained is determined by the position of weight I08. While there are various factors (such as variations in the forced draft, changes in the direction and velocity of the wind and atmospheric changes) which constantly tend to vary the combustion chamber pressure, such variations in these factors are immediately compensated for by the beam I04 and its associatedbecomes stalled or overloaded. If this circuitv breaker opens, the fuel valve and dampers remain in the last position of adjustment, and an alarm may be provided to notify the operator that the circuit has been broken. This alarm may be of any suitable type, visual or audible, or both, and should, of course, be operated by an independent current source so that it will also warn the operator if the electric power for the instrument fails.

The door 51 may carry the main line switch ,20I, preferably of a thermal overload type, and also a selector switch 2I0. The selector switch may be provided with four positions-oif, manual, semi-automatic, and automatic.

In the off position of the selector switch, none of the circuits in the instrument is energized, and there is possible neither an automatic, semi-automatic, or manual control of the furnace from the control cabinet.

When the selector switch is in the manual position the circuits controlled by the beams 62, I6 and I04 are not energized. However, the fuel control valve, the forced draft damper, and the induced draft damper may be manually operated from the control cabinet. On door 58 is located a switch 220, on door 59 is located a switch 255, and on door 6| is located a switch 255'. These switches provide for the manual control of valve 6, and dampers 35 and M, respectively. The button of each switch is resiliently mounted to normally remain in the off position, but may be pivoted in one or the other direction to actuate the motors 50, 40 and 46 in a forward or reverse direction.

When the selector switch is in the semi-automatic position, the circuits controlled by the beams I6 and I04 are energized, but the motor 50 remains under manual control. By this means the operator may manually control the generation of steam, by regulating the feed of fuel, but the amount of air admitted to the furnace through the forced draft wind tunnel will be automatically controlled in accordance with the fuel supply, and also the combustion chamber pressure will be automatically maintained constant. The manual and semi-automatic operation of the unit is particularly helpful when starting up a cold boiler and bringing the plant up to normal operating conditions. By the manual switches 220, 255 and 255, the valve 6 and dampers 35 and M may be adjusted to the desired positions prior to lighting the burners, and then when the burners are lighted, the selector switch may be turned to the semi-automatic position. The operator then controls the combustion to get the steam to the proper pressure, at which time the selector switch may then be rotated to the automatic position.

When the selector switch is turned to the automatic position, each of the circuits controlled by the beams 62, I6 and I04 is energized and thereby the unit operates to fully and automatically operate the furnace.

A modified arrangement for the contacts of beams I6 and I04 is shown in Figure 8, which, as a matter of fact is preferable in view of the added safety factor. It will be appreciated that the contacts are liable to accumulate dirt or become worn out, and in Figure 8 I have shown two sets of contacts for use with each of the beams I6 and I04, and, if desired, may be employed with beam 62.

I shall describe the figure with reference to beam I04, it being understood however that the arrangement on beam I6 may be identical. In addition to the spring contact II3, which is adapted to engage screw contacts H4 and H5,

trol elements.

main body of beam I04, and which forms in effect a beam contact. This block is connected to the conductor (not shown) of beam I04, to which v the flexible contact H3 is likewise connected. The block I2I is adapted to engage contacts I22 and I 23, which it will also be noted are adjustable.

The contacts H4, H5, I22 and I23 are so adjusted that upon oscillation of beam I04 contact H3 will. first engage either contact H4 or H5. However, a slightly further movement of beam I04 will serve to bring block I2I into engagement with either contact I22 or I23, the flexible con-' tact H3 bending during such increased movement. It will therefore be seen that contact H3 is the one which will normallyestablish the desired. circuit, but if this contact should become dirty, worn, or out of adjustment,contact block I2I assures an establishment of the desired circuits Both contacts H4 and I22 are connected to line 246, while contacts H5 and I23 are both connected to line 236', such lines being hereafter referred to in more detail.

While the type of electric circuits for use in this device will of course be optional, in Figures 3 through 6. specific circuits have been shown which may be employed for the individual con- In these figures the circuits which are shown as closed, are indicated by heavy lines, while the open circuits appear in lighter lines.

It will be noted that with respect to the circuits for the forced draft and induced draft control motors, relays are preferably employed so thatthe load on the actual circuits which are opened and closed by the beam contacts 85 and H3; may be kept small. This, of course, insures longevity of these contacts,

In- Figure 3, current flows from a source of current 200, marked line on the drawings, through the thermal overload switch 20I provided with fuses 202, through a conductor 203 to the thermal overload circuit breaker 204. From the circuit breaker 204 current flows through the solenoid of an alarm relay 205 and thence back to the line switch 20I- through conductor 205'.

Thecircuit just described is of course normally closed during the whole time that the switch 2M or the circuit breaker 204 is in the On position. The alarm relay 205 is adapted to actuate upon failure of line current or breaking of the circuitby the circuit breaker 204. When the alarmi're'lay closes, it closes a circuit from a separate source of current, such as a wet or dry battery 206, to operate an alarm 201, which, as

above stated, may be of the visual or audible, or both, type.

From the line switch 20I, current also flows througha conductor 208 to a contact point 200 of the selector switch ZIIJ. As pointed out above, manipulation of this selector switch is adapted toclose circuits for various operations such as manual, semi-automatic, and automatic. In Figure 3, the circuit is closed between contact point 209 and a contact point 2H to establish the automatic circuit. Current from there flows through conductor 2 I 2 to the contact I53 on beam 62.

As shown in Figure 3, the steam pressure has dropped, due for example to additional load, and contact isestablished between contacts 68 and 12. The current then flows through conductor 213 to the winding of the motor 50, which will operate to open the fuel valve 6. From the motor it flows through line 2I4 to circuit breaker 204 and thence back to the line 200. Should any adther ditional load of current occur in this circuit, the breaker 204 will operate to break the circuit and thereby sound the alarm 201.

The above described circuit is shown in this figure in heavy lines, and this circuit increases the amount of fuel fed to the furnace. Assuming that the beam 62 is in balance, should the steam pressure in the boiler rise above its predetermined pressure, the circuit will be as just described except that thecurrent will flow from contact 68 through contact I3, as shown by the light line 2l5, to the other winding of the motor 50'. This of course will operate the motor in a reverse direction to close the fuelvalve 6.

Should it be desired to manually control the fuel feed, the selector switch 2I0 is manipulated to the manual position shown in Figure 4, closing circuit through contact points H6 and 2H. As above mentioned, the fuel feed is manually controlled when the selector switch is in eimanual or semi-automatic positions. Current then flows from the line switch 20I through conductor 208, bridged contacts 2I6 and 2H, and conductor 2I9 to the blade of the manual switch 220. This switch may then be thrown to operate the motor 50 either to open or close the fuel valve 6. As shown in the heavy lines of Figure 4, the circuit is closed to the increase contact point 22I of switch 220, the current flowing through conductors 222 to the forward winding of motor 50.

To reverse the motor, the blade of the switch 220 is thrown to close contact to the decrease point 223, current then flowing through lines 224 to the reverse winding of the motor.

It will be noted that even when the fuel valve motor 50 is manually operated, the alarm relay and breaker circuit still remains normally closed. This is a single circuit of course for the entire control, and, while I have shown it in connection with each of the several wiring diagrams of Figures 3 through 6, I will not repeat its description.

Figure 5 shows schematically the circuit for operating the forced draft damper. In this figure, current flows from the line switch 20I through conductors 208 and 230 to contact point 233 of the selector switch 2 I 0. In this figure the selector switch is shown as in the automatic position, current flowing through to contact point 234' and thence to 234. From there it flows through line 235 to the beam 16. As above discussed, this beam is adapted to be rocked by variations in fuel pressure, and, as shown in this figure, the fuel pressure is above normal, throwing contact 85 into engagement with contact screw 81. The current then flows through line 236 to the solenoid 231 of a relay 238 (legend on the drawing increase relay). These relays are employed, as above pointed out, for the purpose of avoiding heavy loads through the beam contacts. The relays may be located in the compartments of their respective beams, or they may be mounted on the inside of the compartment doors. a

From the relay solenoid 231, the current flows back to the power line through lines 239 and 240, circuit breaker 204 and line 203.

When the solenoid 231 is energized, the armature 24l of the relay closes contact between the line'242, connected with the line switch 2M, and a conductor 243 which leads to the increase winding of the motor 40 which operates to open the forced draft damper 35. From this winding,

current flowsback to the source of current through lines 240 and 203.

Should the feed of fuel be decreased, or perchance the forced draft exceed its ratio to the fuel feed for some reason, the beam 16 moves so that contact 85 engages contact 86. The circuit so established is in part identical with the circuit just described with the following exceptions: From contacts 85 86 the current passes through line 246 to solenoid 241 of the decrease relay 248, thence through line 239, to lines 240 and 203 to the line switch 20L Energization of solenoid 247 establishes a circuit which passes from the switch 20| through line 242 to the armature of the relay 248. From the armature the current passes through the line 249 to the decrease winding of motor 40, and thence back by way of lines 240 and 203 to switch 2!. This serves to close the damper 35 to reduce the forced draft.

Should manual operation of the forced draft damper be desired, selector switch 2H] is rotated to the manual position. This serves to close a circuit through contact points 25l and 252 of the selector switch, the current then flowing from line 208 through line 253 to the blade 254 of the manual switch 255. It will be observed that this switch may be operated to continue the circuit through coil 23'! of relay 238, or to coil 24! of relay 248; and thence, in either event, returning to the switch 20! by Way of lines 239, 240 and 203. Obviously, the manual actuation of one or the other relay establishes the respective motor operating circuits as described above.

In Figure 6 there is disclosed a diagram of the circuit which may be employed with the stack damper control beam. This circuit is similar to that shown in Figure 5, except merely that the selector switch 210 is here shown in semi-automatic position. In the semi-automatic position of the selector switch, the necessary contacts are closed to automatically operate both the forced draft and stack dampers, as above mentioned, and to permit of manual operation of the fuel valve.

However, the circuit which operates the stack damper motor 46 is similar to that shown in Figure 5, and therefore the same numbers, primed, are applied to this figure. It is not believed necessary, therefore, to repeat the description of,

the circuit, which is set forth above in connection with Figure 5.

While this invention has been described with respect to a single furnace, it will be appreciated that it may be applied to a battery of furnaces. As heretofore pointed out, it may readily be applied to a battery of boilers which receive their fuel through a common control valve, air through a common wind tunnel, and which discharge their flue gases into a common breeching. In such event the manometer I4 will be responsive to the boiler pressure in the common header from the battery of boilers or the pressure in one boiler which might be selected as a pilot for the battery. The manometers l8 and I!) will be responsive to the fuel pressure in the fuel header; the manometer 21 would be responsive to the pressure of the forced draft; and the manometer 34 may respond to pressure in any one of the furnaces serving as a pilot. As pointed out, with such an arrangement proper valves and dampers are employed to maintain the desired ratio between the quantities of fuel and air supplied to the respective furnaces and the flue gases exhausted therefrom.

In the event that the boilers of a battery should receive their fuel supply through separate control valves, separate fuel control beams should be provided which would be responsive to the steam pressures of the boilers and their respective fuel pressures. Likewise, if the boilers of the battery should receive their supply of air from separate wind tunnels, then separate forced draft control beams should be provided, such beams being responsive to the fuel pressures and forced draft pressures of the respective boilers. And finally, if the boilers of the battery discharge into separate stacks, separate beams responsive to the pressures in the respective furnaces should be provided to control the dampers in the stacks.

From the foregoing it will be observed that an instrument is provided for controlling combustion which operates on a principle of balancing various factors against one another. These factors are the pressures of the several control factorsthe heated medium, the fuel, the combustion-supporting air, and the pressure in the combustion chamber. The change in the pressure of any one of these factors disturbs the balance of the several control beams which instantly readjust the valves and dampers to re-establish the ratios between the several pressures.

For instance, upon any variation in the steam pressure in the boiler, :there is an immediate change in the rate at which fuel is supplied, and this change in fuel feed in turn instantly changes the forced draft to maintain the ratio between fuel and air to insure maximum combustion efiiciency; and the change in forced draft effectuates a change in the stack damper to maintain the combustion chamber pressure the same.

It will also be noted that each of the control factors controls itself. In other words, a drop in steam pressure is compensated for by a change in combustion. With a given setting of fuel valve 6, if there should be any change in the fuel head, this will be immediately compensated for by a change in the opening of valve 6 so as to maintain a fuel input sufiicient to insure the desired steam pressure; with a given fuel feed, a change in the forced draft air supply, for any reason, will automatically be compensated for by a change in the position of damper 35; the position of the furnace outlet damper 4! is being constantly shifted to compensate for minute changes in any of the factors determining the combustion chamber pressure.

It will be appreciated that the invention is of relatively simple construction, presenting little opportunity for the device to get out of order, and with a minimum of movable parts. It is therefore economical both in construction and operation, and the simplicity of its operation insures a functioning with a negligible amount of supervision.

There have heretofore been pointed out certain modifications which may be made in the specific embodiment herein described. These, however, are to be taken as exemplary, for the basic concept will find numerous other obvious modifications which fall within the scope of the invention as defined by the appended claims.

I claim:

1. In a furnace having control factors, the combination of a movable beam which controls the rate of fuel being fed to the furnace by actuating a motor which operates from a source of power which is independent of the medium being heated, said movable beambeing motivated by two variable means, one of which is actuated directly by the change in the condition of the medium being heated and the other being actuated directly by the change in the pressure of the fuel being fed into the furnace, a second beam to control the supply of air being fed to the furnace by actuating a motor which operates from a source of power which is independent of the medium being heated, said second beam being motivated by two variable means, one of which is actuated directly by the pressure of the fuel being fed to the furnace and the other by the static pressure of air being fed minated.

2. In a furnace having control factors, the combination of a beam, the movement of which makes and breaks an electrical circuit thereby controlling the operation of a motor, the operation of which varies the position of a fuel valve, said movable beam being motivated by two variable means, one of which is actuated directly by the change in the condition of the medium to be heated and the other is actuated directly by the change in the pressure of the fuel being fed to the furnace, a second beam, the movement of which makes and breaks an electrical circuit and thereby controls a motor which varies the position of the damper in the air intake tunnel of the furnace, said second beam being motivated by two variable means, one of which is actuated directly by the pressure of fuel being fed to the furnace and the other by the static pressure of the air being fed tothe furnace, a third beam, the movement of which makes and breaks an electrical circuit thereby controlling the operation of a motor, the operation of which varies the position of a damper in the stack of the furnace, said third beam being motivated by variable means which are actuated by a change in pressure in the combustion chamber of the furnace, a switch to shunt the above-mentioned electrical circuits thereby forming a new circuit and eliminating the control of all of the beams over the factors of combustion which they are designed to control, a second switch to connect the newly formed circuit with the source of power, and means to control the factors of combustion manually by means of the newly formed electrical circuit.

ROBERT LEWIS. 

